LTC3816_15 Datasheet, PDF (20/44 Pages) Linear Technology – Single-Phase Wide VIN Range DC/DC Controller for Intel IMVP-6/IMVP-6.5 CPUs

LTC3816
APPLICATIONS INFORMATION
Note that the value of R_DCR must account for its temperature
coefficient, which is approximately 0.39%/°C.
The current limit architecture of the LTC3816 allows short
durations of instantaneous overload. Upon power-up, the
current limit threshold is set to 1×, equal to I_LIMIT . The
load is limited to I_LIMIT until the switcher output reaches
its V_BOOT potential. Beyond this point, during the VID DAC
slewing interval, the I_MAX sourcing current automatically
switches from 10µA to 20µA and the current limit threshold
increases to 2× to enable the output capacitor voltage to
track the DAC transition. If the controller detects that there
is an overload condition when the DAC is not slewing, the
current limit threshold increases to 2× for a duration of
45µs. If the overload interval is shorter than 45µs, the IC
allows another overcurrent event within the next 630µs,
as shown in Figure 6a. However, if an overload occurs
within the 630µs following the second event, the controller
current limits, as shown in Figure 6b.
If the overload condition persists for more than 45µs,
the LTC3816 allows the 2× current limit to continue for
CURRENT LIMITED
20µA
I_IMAX
10µA
45µs
45µs
45µs
2s
1s
I_LOAD
<45µs
<45µs
<630µs
>630µs
<45µs
3816 F06a
Figure 6a. Permissible Overload
another cycle. After 90µs, the I_MAX current returns to 10µA,
and the output load is limited to 1× for the next 630µs as
shown in Figure 6c. Figure 6d shows the condition when
a repetitive overload event triggers current limit.
Figure 6e shows that at any instant, if the load current
is above 1× for more than 90µs, or higher than 2×, the
controller enters current limit. Under this condition, the TG
duty cycle is reduced and the SS capacitor is discharged
CURRENT LIMITED
20µA
I_IMAX
10µA
2s
1s
90µs
I_LOAD
45µs < t < 90µs
>630µs
45µs
<45µs
3816 F06c
Figure 6c. Allowable Longer Overload Condition
CURRENT LIMITED
20µA
I_IMAX
10µA
90µs
2s
1s
I_LOAD
45µs < t < 90µs
<630µs
<45µs
3816 F06d
Figure 6d. Allowable Longer Overload Condition,
Followed by Repeated Overload Triggers Current Limit
CURRENT LIMITED
20µA
I_IMAX
10µA
45µs
45µs
2s
1s
I_LOAD
<45µs
<45µs
<45µs
<630µs <630µs
3816 F06b
Figure 6b. Repeated Overload Triggers Current Limit
20
CURRENT LIMITED
20µA
I_IMAX
10µA
90µs
45µs
2s
1s
I_LOAD
>90µs
>630µs
<45µs
3816 F06e
Figure 6e. Long Overload or Excessive Loading
Triggers Current Limit Condition
3816f